Micra k12 sport power issue cat problem

My 2006 Micra sport+ k12 has an issue whereby the power is lacking, particularly on 4th and 5th gears.
There is an "air" noise coming from the engine bay at 3.5k revs and above in the higher gears when trying to accelerate.
She was doing this before and then the car totally lost power and would not run.
The exhaust manifold seemed to have alot of pressure so I took it apart and the cat and seen the cat was destroyed and part of it was blocking the downpipe, stopping the car from breathing.
I changed the cat for a used good part and all has been good for a month but now the symptoms have started again.
Surely I can't need another cat? But if I do then something else must be causing the destruction of the cats.
Does anyone have any ideas, assistance they can give to sort this out please?
There are no codes coming up on the obd2 to give me an idea at all
Thank you in advance everyone
 
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